Social-emotional competence, coping, and vulnerability are assessed in a longitudinal study of young children with an affectively ill parent. The sample consists of 44 predominantly middle-class families. Children of mothers with unipolar depression and normal mothers are seen at two and at five years of age. They are observed in a laboratory setting in interaction with their mothers, adult strangers, and familiar playmates. The affective environment is varied experimentally to assess children's social-emotional responses. An earlier investigation using similar procedures to study two-year-old children wtih a bipolar parent indicated significant problems in the quality of interpersonal relations, ability to empathize with playmates, and in resolution of hostile impulses. Although less severe disturbances was seen in children with a unipolar depressed mother, these children also differed from those from control families. Relative to controls, children with a unipolar depressed mother were unlikely to engage in physical aggression with their playmates, likely to show preoccupation and upset when exposed to conflict and distress in others, and likely to be somewhat less spontaneous in their expression of emotions. Comparisons will be made of the children's behavior at two and five years in order to explore processes associated with continuities and discontinuities in patterns of coping in children with an affectively ill parent.